The goals of this core are to provide laboratory support for in situ (primarily immunohistochemical) assays, serve as a collaborator/consultant in investigations of breast cancer biology/pathology, and facilitate translational applications of potentially important assays on breast tissue samples to investigate their clinical significance. A major responsibility of this core is to work closely with Dr. Smith's project to investigate markers which may identify DClS with a high risk of recurrence or invasion. Markers associated with either tissue invasion or metastasis, as well as cellular proliferation (i.e. factors which affect the cell cycle, cellular division or death) will be emphasized. The expression, or lack thereof, of these will be investigated in benign, premalignant, malignant in situ and invasive breast epithelium. Markers which can be associated with an aggressive phenotype of ductal carcinoma in situ (DCIS) will be tested on retrospectively accrued cases of DCIS with or without disease recurrence and/or progression. This core will also serve as an additional tissue resource providing fixed-embedded archival human breast tissues containing specific lesions. Review of breast pathology, histologic and immunohistologic slide interpretation will also be provided.